Many anatomic structures in the mammalian body are hollow passages in which walls of tissue define a central lumen, which serves as a conduit for blood, other physiologic fluids, nutrient matter, or waste matter passing within the structure. In many physiologic settings, dysfunction may result from a structural lumen which is either too large or too small. In most such cases, dysfunction can be relieved by interventional changes in the luminal size.
Thus in surgery, there is often a need to adjust the internal circumference of an orifice or other open anatomic structure to modify the size of the orifice or opening to achieve a desired physiologic effect. Often, such surgical procedures require interruption in the normal physiologic flow of blood, other physiologic fluids, or other structural contents through the orifice or structure. The exact amount of the modulation required for the desired effect often cannot be fully appreciated until physiologic flow through the orifice or structure is resumed. It would be advantageous, therefore, to have an adjustable means of achieving this modulating effect, such that the degree of modification could be changed after implantation of a device, including after the resumption of normal flow in situ.
One example of a dysfunction within an anatomic lumen is in the area of cardiac surgery, and specifically valvular repair. Approximately seven hundred thousand open heart surgical procedures are now performed annually in the United States, and as many as twenty percent of these operations are related to cardiac valves. For example, mitral valve repair has become one of the most rapidly growing areas in adult cardiac surgery today.
Two essential features of mitral valve repair are to fix primary valvular pathology (if present) and to support the annulus or reduce the annular dimension using a prosthesis that is commonly in the form of a ring or band. The problem encountered in mitral valve repair is the surgeon's inability to fully assess the effectiveness of the repair until the heart has been fully closed, and the patient is weaned off cardiopulmonary bypass. Once this has been achieved, valvular function can be assessed in the operating room using, for example, transesophageal echocardiography (TEE). If significant residual valvular insufficiency is then documented, the surgeon must, in conventional procedures, re-arrest the heart, re-open the heart, and then re-repair or replace the valve. This increases overall operative, anesthesia, and bypass times, and therefore increases the overall operative risks.
If the prosthesis used to reduce the annulus is larger than the ideal size, for example, mitral insufficiency may persist. If the prosthesis is too small, for example, mitral stenosis may result. The need exists, therefore, for an adjustable prosthesis that would allow a surgeon to adjust the annular dimension in situ in a beating heart under TEE guidance or other diagnostic modalities to achieve optimal valvular sufficiency and function.
There remains a need in the art for methods and apparatus that will facilitate post-operative adjustment of a prosthetic implant to reduce the diameter of such a mitral annulus in a percutaneous or other minimally invasive procedure, while still achieving clinical and physiologic results that are at least the equivalent of the yields of the best open surgical procedures for these same problems.